Process for desulphurizaton of iron and steel



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H. KOPPERS PROCESS FR DESULPHURIZATION oF IRON AND STEEL Filed July 8, 1921 #n A w V @iff @@@nWQ/ A wwg@ @www A @va V i Q A V @@@w V M %7 v .//mmwL Patent @et 23, "123.l

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HEINRICH KOPPERS, 0F ESSEN-RUIHR, GERMANY, ASSIGNOR T0 THE KOPPERS DE- VELOPMENT CORPORATION, OF PITTSBURGH, PENNSYLVANIA, .A CORPORATION OF PENNSYLVANIA.

' raocuss ron DEsULrHuRIzAToN or mou AND STEEL Application led July 8,

To all whom t may concern:

Be it known that L HEINRICH KoPPERs, assignor to The Koppels Development Corporation, a corporation of Pennsylvania. a citizen of Germany, residing in Essen-Ruhr, Germany, have invented a nevvr and useful Improvement in Processes for Desulphurization of Iron and Steel, of which the following is a specification.

This vinvention relates to an improved process for the desulphurization of iron and steel in large quantities.

The main German application K. 67087 VI/18b relates to a process for the desulphurization of large iron and steel quantities,

according to which the liquid. iron, finely distributed, is made to pass through a layer of slag in which, by means of the constant im mersion of carbon at ahigh temperaturera releasing of calcium '(C in combination with alumina. calcium slag yields CaC2, Ca, Al, etc., and these substances .have a deoxidizing effect) is brought about which causes the sulphur from the iron to combine to form calcium sulfide and the oxygen to form C`a0.

The calcium sulfide itself is in or under the slag, and is soluble in this but not in the metal itself, so that in this manner the completeremoval of the sulphur and the oxygen can be brought about. (Compare Stahl and Eisen, 1908, page 873.) For carryingl out this process, a device is usefll which consists ofa fire-proof receptaclein which, by

means of siphonlike overflows uniform liquid levelsl are constantly maintained for the uid iron, While, by means of a lid closing the vessel at the top and perforated aftery the manner of va sieve, the pressing-in of the coke piecesintroduced into the slag is insured on the one hand,'and as line a distribution as possible is effected on the other hand for the liquid: ironcharged at the top,

' so that it is possible for thes'ame to percolate through the slag in thin streams.

Y The present invention concerns an improved form of embodiment of the same idea which constitutes, both as regards the process andalso more. particularly with refer- Y ence to the arrangement to be applied thereto, a valuable simplification, inasmuch as the process can be carried out, for instance. 1n an ordinary hearth oven. The deoxidizing .and desulfurizing of the iron in the hearth oven has taken place heretofore bythe use'` 1921. Serial No. 483,146.

of deoxidizing agents, such as calcium carbide, ferromanganese, ferrosilicon, spiegeleisen, aluminum and similar'expensive substances, to be introduced from the outside.

In this connection, `While employing several hearth ovens or tilting hearth ovens, the operation is 'carried out by first eliminating, by means of oxidizing the iron bath, the impurities which can be removed in this manner; the bath thus prepared is transferred to another hearth oven, or the slag is discharged entirely and the bath provided with new slag of high lime content. By int-roduclng vthe reducing substances, a deoxidizing and desulfurizin is then brought about.

When using ca cium carbide, this remains j oatmg in the slag. whereby the metal oxides l in the same are reduced and the metal passes 1nto the steel bath. Substances like ferrosilicon sink thgough the slag and are dissolved inthe steel bath. Manganese, added as ferromanganese, also sinks down immediately through the slag and. is dissolved in., the bath, while existing sulphur goes into'.

the slag partly as manganese sulfide. A reaction of the sulphur compounds with the lime ofthe slag cover does not take ,place to Aany appreciable extent, unless the presence of the silicon facilitates the reaction to CaS. t

gether in the literature on the subject (compare Dichmannz Der basische Herdofenprozess, ages 126, 127).

In the e ectric'furnace the sulphur is eliminated to the point of leaving only traces, an

oxidizing effect being aimed at 1n the first place by means of the addition of oxides and the' resultant slag then being replaced by a new basic slag. The deoxidizing takes/place with ferrosilicon, While previously, forJ ther purpose of increasing the carboncontent, if necessary, petroleum coke, pieces of electrodes orother carbon are added, and the slag cover Jis covered with carbon or coke v powder for the purpose .ofl producing a neutral atmosphere.' If the ferro-silicon is replaced by ferromanganese, a desulphurization is notobtained any more than is the case if the slag contains more than 2% of metal oxides.

By this invention, all that is aimed at, the same as according to the main application, is to release calcium through the medium of carbon dipping into the slag, the calcium combining with the sulphur and forming calcium sulfide. For that purpose, the iron bath, after being purified as usual from phosphorus, manganese, silicon, etc., is to be transferred, free from sla remnants, tothe hearth oven, where a basic slag blanket is produced. The immersion of the carbon into this highly heated slag cover is effected by adding a specially prepared form ofcarbon whose specific gravity coincides substantially with that of the slag.

. ln addition to the transfer -of thesulphur` as calcium sulfide into the slag, there also takes place at the same time acombining of the still existing oxygen with calcium and then with the carbon which then passes away in gaseous form as carbon monoxide The calcium sulfide remains inthe slag layer as long asva neutral atmosphere prevails above the latter. ln this connection, the freedom` from sulphur of the heating gas plays no part. llt is true the slag will absorb sulphur from heating gas rich in ,sulphur, but this will not go to the iron because the slag is free from heavy metal oxides, principally` ferrous oxide. The calcium eliminated from the slag by direct reduc- -tion floats inside of the slag or forms a layer between the iron and slag. For bringing about a better reaction between the iron and calcium, the iron bath in this connection can be agitated or caused to bubble by the usual means, so that all of its parts may reach the surface at one time or another. A high temperature is indispensable for the formation of the calcium from the CaQ.

After the liquid bath has thusbeen rid of sulphur and oxygen, it is possible to supply to it, if alloying'is the aim, the respective substances to be admixed, be they carbon, silicon, tungsten, chromium or the like. lin order to avoid a burning of the carbon on the one hand, however, and its dissolution by carbonio acid withA the resultant lowering in temperature on the other hand, the carbon must be rendered difficult of combustion. 'lhese two qualities of the higher specific gravity and the reduced combustibility can. be obtained for coke by superheating it,

whichcauses its cellular structure to become smaller or finer and its specific gravity to increase, while by expelling the last remnants of hydrogen its combustibility isalso diminished. lfn place' of such coke, carbon bricks or graphite can also be used. The carbon is best given whose'size is governed by the thickness of the slag layer which latter itself has to have a certain height. For that purpose coke is the shape of bricks ground fine and pressed underhigh pressure and with a suitable binding agent, such as tar, so as to form bricks which are given a specific Weight of about 1.8, thus becoming approximately as heavy as the slag itself. ln order 'to increase the effective area or surface, without reducing the dimensions of the bricks, these can be provided with suitable perforations.

'llhe entire process permits of the layer of slag serving for the desulphurization to be used over again at any time by always revivifying it. For that purpose, air is conducted over or through the slag cover, in which case the calcium sulfide burns up and forms sulfurous acid and the S passes off as S02 with the air. ln this manner this impurity of the iron bath is discharged in gaseous form, while revivifying or regenerating the slag bath. Sincein this connection, however, an oxidizing of the sulfide into sulfate may also take place and the latter would again form iron sulfide with the iron, the regeneration of the slag blanket is effected each time after running oii the iron bath.

An arrangement suitable for carrying out the process described is reproduced in the drawings forming a part-of this application, in which Fig. 1 is a longitudinal vertical section and Fig. 2 is a plan View `of the hearth and iron bath and slag cover. Fig. 3 shows, through the iron above the same.

rllhe hearth oven 10, made in the wellknown manner, is provided with the lining 11 and heated by means of the flues 12, and contains the iron bath 13, which supports the comparatively heavy slag layer 14. lnto this sla layer 14 the coke or carbon pieces 15 are ipped in such a way that they just float in it.. rllhe spaces between the different coke pieces 15 can be filled by means of coke powder sprinkled into the slag layer so as to protect the surface of the latter.`

q rllhe plan described has nothing to do with the practice, already mentioned, of covering the slag layer 1n electric furnacesyfor the purpose of avoiding oxidizing, since the operations herein described do not take place in that'process. This, if for no other reason, is shown by the fact that here, too, such a covering of the surface with carbon powder is suitably used as` an additional step for the same purpose. @nly when working according to the instructions herein contained, is the calcium systematically released as the cheapest and most effective means for desulfurizing and deoxidizing.

1. A process for desulphurizing large quantities of iron and steel which consists in covering the bath, after the bath has been freed in the usual manner from phosphorbath and the slag layer on a larger scale, a partial section ter these elements havebeen freed, with av new, thick, highly basic slag into which specially prepared carbon of approximately the same specific gravityu as the vslag is dipped, for the purpose of combining with sulphur to form calcium suphide b releasing calcium under the influence o high temperatures and with a neutral atmosphere, thus removing at the same time the last traces of oxygen as carbon monoxide. Y

2. A process according to claim 1, characterized by a lform of carbon being used which, owin to superheating, possesses a higher specic gravity and such low combustibility that both its combustion by air and its reduction to carbonio acid, with resultant lowering in temperature, are lessened and yet, in conjunction with the wellknown surface covering of the'slag layer by means of carbon owder, the requisite neutralit of the gas ayer above the slag is obtaine l 3. A process according to claims 1- and 2, characterized by 'theslag layer being regenerated at any time by passing air-over or throughvit, in which connection the sulphur isdischarged as sulfurous acid, while, in order to avoid a resulfurizing of the iron ba'th, the latter is first run olf.

4. A process according to claim 2, characterized by the carbon being given the shape of bricks whose dimensions corresponds to the height of the slag layer and which are made lof finely ground coke with a binding a ent such as tar under high pressure in w ich connection, for the purpose of increasing the-surface, the bricks vided with perforations. 5. Aprocess for desulphurizing iron and steel, consisting in separating from each other the iron bath and its first yslag cover, and then covering the bath with a basic slag containingPcalcium and 'pieces of densified can be pro-y carbo'n, and separating from the bath sulphur as calcium sulphide,and oxygen as carbon monoxide.

6. A process for desulphurizin iron and steel, consisting in separating rom each other the iron bath and its first slag' cover, and then covering the bath with a basic slag containing calcium and pieces of carbon of relatively `high specific gravity and low combustibility, and witha carbon powder covering, and separating from the bath sulphur as calcium sulphide, and oxygen Aas carbon monoxide.

7. A process for desulphurizing iron and steel, consisting in separating from each other the iron bath and its rst slag cover, and then covering the bath with a relatively heavy and. thick basic slag containing calcium and pieces of densified'carbon, and separating from the bath sulphur as calcium sulphide, and oxygen as carbon monoxide, and removing .sulfurous acid from and revivifying said basic slag cover by the use of air, and re-using it forthe same purpose.

8. A process for desulphurizingironand steel, consisting in separating from each other the iron bath and its first slag cover, and then covering the bath with a basic slag containing calcium and perforated pieces of densified carbon'made of finely ground coke and\a binding agent under hi h pressure,

cium sulphide, and oxygen as carbon monoxide.

9. A process for desulphurizin' iron and and separating from the bath su phur as caly steel, consisting in separating rom each other the iron bath and its lirst slagY cover, and then covering the bath with a basic slag4 containing calcium and pieces` of densified carbon, and separating from the bath sulphur as calciumv sulphide, and oxygen as carbon monoxide` and adding alloying material to the metal in said bath.

" l HEINRICH KOPPERS. 

